The U.S. Supreme Court ruled in 1997 that the federal government cannot force state officials to participate in the background check system for gun ownership, leading to the omission of likely millions of names.

Nineteen states have submitted fewer than 100 records of those with mental illness, while Rhode Island has submitted none, the New York Times reports. In addition, 30 states do not submit noncriminal records, such as positive drug test results for probationers.

Gaps in the database didn’t appear to be a factor in the Sandy Hook grade school shooting in Connecticut, they have been linked to the Virginia Tech massacre. A judge had declared the Virginia Tech gunman mentally ill, but the information was not given to the FBI.

Virginia has since stepped up its submissions to the database, the Times says, “but other states have not taken similar steps because of lack of political will, technical obstacles and state privacy laws.”

The story points out a different gap: the background check requirement applies only to licensed gun dealers, not private sellers who account for 40 percent of gun sales.